In terms of quality or how complex it is to read? (and this will then have to wait for me to re read a few pages of each - I don't tend to pay that much attention to style in non-fiction). I vaguely remember Castelot's style being more conservative, but not really heavy going.

I enjoy Bertière a lot. She's one of the few historians I buy new books from almost systematically (it would really take a subject I care nothing for to make me skip one). Her latest (?) was a really great biography of Mazarin, probably the best of the four or five I've read so far (and the only one written by a woman). Again, one of her strengths really is to combine good synthesis/analysis with good narrative.